In the activities of drilling for oil there is an operation consisting in lining the drilled well by a pipe firstly to retain the formation and secondly to contain the pressure of a blowout should this occur.
At present, such "casing" is made of metal and is lowered into the well progressively as work proceeds, by adding a section of pipe to the top of the column of pipe that has already been lowered into the well.
The same applicant's U.S. patent application 07/946,423, of Nov. 6, 1992 now U.S. Pat. No. 5,337,823, proposes a system of casing in which the wall of the pipe is radially deformable, such that the casing can be lowered down the well in its folded state, i.e. with reduced radial size; once it is in place, it is inflated so that its wall regains a cylindrical shape. The annular space between the formation and the pipe is then filled with cement. The advantage in such a system lies in the fact that each successive length of casing is formed during drilling with pipe of the same diameter, the folded pipe being able to pass through the unfolded pipe as previously installed. The consequence of such single-diameter casing is a well that is always of the same, relatively small diameter, resulting in economies in relation to tools, to drilling time, and to the volume of drilled material.
Before use, the casing is stored on large reels, in the folded state, and thus in a relatively small volume, much smaller than that occupied by conventional casing.
A completed casing, whose length may vary from some tens of meters to several kilometers, is prepared by pre-assembling a plurality of coupled sections end to end so as to obtain the desired length, which is then stored on a reel, awaiting placement in the well.
It has accordingly been necessary to provide means for effecting this coupling, while preserving the ability of the pipe to be radially deformed. These means should also be releasable. On site, it is often necessary to adjust the length of the casing to be lowered down the well depending on the length of the drilling actually effected, which can exceed or fall short of the expected target, which target has already determined the length of the casing to be prepared. It is thus necessary to increase or reduce this prepared length--and at the drilling site. To do this, a coupling is released to remove the excess length (or the special endpiece which this kind of casing also includes) and an additional length or the special endpiece is then connected.
The present invention thus concerns a pipe equipped with releasable coupling means and a use of this pipe in oil well casing in accordance with U.S. patent application 07/946,423 now U.S. Pat. No. 5,337,823.